Recently, a hybrid vehicle which reduces an amount of carbon dioxide emissions and is practical is attracting attention.
Specifically, the conventional internal combustion engine used for vehicles such as automobiles is low in a total efficiency because it is operated in a wide load range and a wide range of the number of rotations of the engine. And when the vehicle is temporarily stopped, the engine is generally not fully stopped but kept in an idling state because it is desired that the vehicle can be started immediately, a trouble of restarting the engine is omitted and the like. And, fuel consumption while idling and exhaust gas produced as a result are issues not negligible in view of environment and energy saving. Particularly, such problems are increasing in city areas where traffic jams are often caused.
Furthermore, when a running speed is largely changed, namely when the vehicle is abruptly started or abruptly accelerated from a relatively slow speed, the engine efficiency may be lowered and the fuel consumption is degraded.
Therefore, a hybrid system which is succeeded and developed from a drive system which combines different types of power used for aircraft, ships and the like has lately attracted attention.
This running system is configured to have a conventional internal combustion engine and an electric motor which is a clean power source within a vehicle and to utilize the advantages of both of them to their maximum extent and also to compensate their disadvantages.
There have been proposed a series hybrid which uses the above two drive sources in series and a parallel hybrid using them in parallel.
There is also proposed a hybrid system which is provided with a distribution mechanism which can use for example a planetary gear mechanism to variably distribute the engine output into two systems as desired.
This system is designed to operate the engine in its best condition in view of efficiency, namely fuel consumption, and if the engine output is excessive in view of a running condition, the excess output of the engine is converted into electrical energy by using the electric motor as a generator and recovered and accumulated in a battery, and if the engine output is insufficient, the insufficient traction is supplemented by the electric motor.
But, production of the planetary gear mechanism requires high precision and it is expensive. And the running traction required depending on running conditions is always based on a balance of the driving force of the engine and the driving force recovered or added by the motor. Therefore, a variety of controls, particularly motor control, becomes complex.
And, the conventional engine vehicle generally has a traction control for controlling to have an optimum traction depending on a road surface condition and to improve gripping performance of the drive wheels so that the drive wheels do not skid (spin) or the vehicle does not become unstable to run due to a bad road or the like.
Specifically, when the vehicle is running along a snowed road or a slippery road surface due to freezing, the drive wheels skid, and its running control is disabled or it cannot run depending on a level of skid or a running posture. Particularly, such tendencies are enhanced when the vehicle is started, accelerated or sharply cornered.
For example, feedback control is performed to decrease a throttle valve opening based on a slip ratio of the drive wheels, braking control of the drive wheels is performed to properly control the driving force of the vehicle so to decrease the skids of the drive wheels.
But, the traction control based on such a mechanical structure delays to respond and is not satisfactory for controlling.
The braking control of the drive wheels is not good in view of energy efficiency. In other words, kinetic energy decreased by braking the drive wheels is lost completely.
Furthermore, when any of the wheels skids in the same way as above, a gripping state of that wheel is resumed normal by the aforesaid skid remedying operation, but a total of running driving forces of all the drive wheels becomes lower than before, and a drive balance is lost. Therefore, the running control is not lost but the running performance of the vehicle is lowered.
Accordingly, it is an object of a first invention to provide a hybrid vehicle which can improve energy efficiency and prevent the running performance from lowering to remedy poor behavior of the vehicle at occurrence of a skid.
This type of hybrid vehicle can run in three ways by the engine only, by the electric motors only and by the engine as well as the electric motors.
The conventional hybrid vehicle generally has an electric motor disposed between the clutch of the engine and the transmission or between the engine and the clutch to transmit a combined force of the engine and electric motor outputs to the drive wheels through the transmission to rotate them.
Therefore, the operations of the transmission and the clutch are common between the engine and the electric motor and almost free from making an improper operation.
Recently, there is developed a hybrid vehicle in which the drive system of the electric motor adopts another transmission line. In other words, the drive system of the engine is connected to the drive wheels through the clutch, the transmission and the like, while the drive system of the electric motor is connected at some midpoint thereof to the engine drive system or directly connected to the drive wheels.
In the hybrid vehicle which has the drive system of the electric motor and connected to the drive wheels through another reduction gear, its operations (selection of forward, reverse and gear change ratio) are different in the running by the engine only, the running by the engine and the electric motor, and the running by the electric motor only. Therefore, it may require two types of operation systems, and those operation systems are sometimes operated erroneously.
Therefore, it is an object of a second invention to provide a hybrid vehicle which can make operations (selection of forward, reverse and gear change ratio) of an engine and electric motors without making a mistake, and the operations can be made rationally, e.g., while the vehicle is running.
The conventional engine-mounted vehicle uses a so-called traction control system (hereinafter called TCS) to control a spin when it is caused as the drive wheels skid due to some reasons such as abrupt start on a road having a low coefficient of friction, a bad road or the like.
TCS controls the engine output or the brakes to control the drive wheels by judging that the drive wheels are spinning in view of a difference caused due to an abrupt increase of the drive wheel speed from the vehicle body speed presumed from the driven wheel speed, back-and-forth acceleration or the like.
Specifically, the engine control system is provided with a throttle (hereinafter called a first throttle) which responds to the accelerator pedal operated by the driver and also a throttle (hereinafter called a second throttle) operated based on the result judged by an arithmetic unit. The second throttle is operated when the speed of the drive wheels exceeds the engine control setting speed determined in view of a difference of speed or the like from the vehicle body speed.
A control system of braking has a brake (hereinafter called a second brake) operated on the basis of a result judged by the arithmetic unit in addition to a foot brake operated by the driver. The second brake is operated when the speed exceeds a brake control setting speed which is determined independent of the engine control setting speed.
And, when the driver opens the first throttle and the drive wheels have skids, the arithmetic unit judges that the drive wheels are spinning if the speed of the drive wheels exceeds the engine control setting speed and lowers the engine output by means of the second throttle to decrease the speed of the drive wheels so to remedy the spins.
And, when the drive wheels have heavy skids, namely the drive wheel speed exceeds the engine control setting speed and the brake control setting speed, a brake fluid pressure of the pertinent drive wheel is increased to control the drive wheel (operation of the second brake).
In addition to the control using the second throttle, there are also available a method of controlling by the arithmetic unit by means of throttle-by-wire and a method of controlling an amount of fuel injection.
Recently, there is also used a function which is called a vehicle stability control (hereinafter called VSC) which detects a lateral acceleration (yaw rate) of the vehicle while steering and turning, changes the torque to the right and left drive wheels or brakes before the vehicle spins in the same way as the above traction control, thereby controlling the stability of the vehicle.
It is also considered to use the above TCS or VSC for the hybrid vehicle. When the engine output is controlled by the TCS or VSC, there is a disadvantage that there is a time lag between the application of control to the throttle and fuel injection and the actual reaction of output due to a factor such as inertia or the like. Therefore, before using the conventional TCS or VSC, it is desired to use the electric motor to control spin of the drive wheel or to control to prevent the spin.
Particularly, when the brake control is made by the TCS, a reaction speed to the control is faster than the engine control, but when a situation to reach the brake control setting speed is continuously made, the brakes generate heat, possibly resulting in fading. In other words, energy is abandoned as heat and a sufficient braking force may not be obtained. Therefore, its use is limited.
Accordingly, it is an object of a third invention to provide a hybrid vehicle and a method of controlling its running which can improve energy efficiency and prevent the running performance from lowering so to make the spin control or spin prevention control of the drive wheels by using an electric motor, both an electric motor and TCS or VSC, or an electric motor before TCS or VSC.
As described above, this type of hybrid vehicle is generally provided with three types of running patterns such as running by an engine only, an electric motor only, and an engine and an electric motor.
To run by the engine, the rotations of the engine are transmitted to the transmission through the clutch, and the drive wheels are driven to rotate by the rotation force converted by the transmission. And, to run by the electric motor or to run by the electric motor and the engine, the rotation torque is increased by increasing the current value of the electric motor according to a stepped-on quantity of the accelerator pedal by the driver, namely an accelerator opening angle.
And, the manual transmission of the conventional hybrid vehicle is generally the one used for an ordinary engine vehicle.
When such a hybrid vehicle which is running by the engine (including the combined use of the electric motor) does not use the engine to go down a long downward slope, the engine brake is generally operating. Therefore, the kinetic energy of the vehicle is partly lost as a mechanical loss of the engine.
Accordingly, it is an object of a fourth invention to provide a hybrid vehicle which can avoid a loss of the kinetic energy.
In the conventional hybrid vehicle, the power transmission of the electric motor is generally effected upstream of the clutch, namely the power transmission is performed through the differential gear. Therefore, the space for mounting the electric motor must be secured, and the number of components to some extent are required.
Therefore, the fourth invention aims to provide a hybrid vehicle that the power transmission of the electric motor is not effected through the differential gear but in the vicinity of the drive wheels so to save the space for mounting the electric motor and to decrease the number of components.